The present invention relates to a process for the preparation of epoxides such as the known 2-(4-chlorophenylethyl)-2-tert-butyloxirane, which can be used as intermediate for the synthesis of the fungicide 1-(4-chlorophenyl)-3-(1,2,4-triazol-1-ylmethyl)-4,4-dimethylpentan-3-ol.
It is known that oxiranes can be prepared by reacting dimethyl sulfide with methyl bromide and then reacting the resulting trimethylsulfonium bromide with carbonyl compounds in the presence of an inert organic solvent and in the presence of a strong base, such as sodium hydride, sodium amide or potassium tert-butylate (See, e.g., Ber. 96, 1881-1890 (1963)).
It is also known that 2-(4-chlorophenyl-ethyl)-2-tert-butyloxirane can be synthesized by treating dimethyl sulfide with methyl bromide in the presence of an inert organic diluent and reacting the resulting trimethylsulfonium bromide with 1-(4-chlorophenyl )-4,4-dimethylpentan-3-one in the presence of a base and also in the presence of an inert organic diluent at temperatures between 0.degree. C. and 60.degree. C. (See, e.g., DE-OS 3,315,510). Relatively pure 2-(4-chlorophenylethyl)-2-tert-butyloxirane can be prepared by this process. However, this reaction requires relatively long reaction times and the yield is not always sufficient for practical purposes. Another disadvantage of this disclosed process is that the preparation of trimethylsulfonium bromide can only be achieved at a relatively low yield of about 75%. The space/time yields in this process only reach values of about 6 g/l h.
U.S. Pat. No. 4,988,829 discloses a process for the production of 2-(4-chlorophenylethyl)-2-tert-butyl oxirane in which a suspension of trimethylsulfonium bromide having a solids content between 10 and 70% is formed by mixing a solution of trimethylsulfonium bromide in a methanol/toluene mixture with heated toluene while distilling off a methanol/toluene mixture. This suspension of trimethylsulfonium bromide in toluene is then reacted with 2,2-dimethyl-5-p-chlorophenyl-3-pentanone in the presence of solid potassium hydroxide, diethylene glycol and water at a temperature between 20.degree. and 120.degree. C. The need to form a trimethylsulfonium bromide suspension and the use of water in the reaction mixture are among the disadvantages of this process.